The objective of this research proposal is to utilize a colony forming cell assay for the purpose of studying growth and differentiation of human lymphocytes. Efforts will be made to study development of both T and B-cell colonies in a methyl cellulose medium. In addition to plant lectins other potential inducers of lymphoid colony formation will be examined. This will include evaluation of supernatants from cultured human tissues such as thymus, thymic epithelium and fetal liver tissue. Serum sources will be tested for colony promoting activity. The role of cellular interactions in colony formation will also be examined. When colony promoting factors are identified, an attempt to characterize the physical properties of these factors will be made. An understanding of regulatory mechanisms important in colony formation and lymphocyte differentiation should provide insight into the problems of differentiation seen in patients with immunodeficiency conditions and in lymphoproliferative disorders. Cells from patients with these disorders will be evaluated for their capacity to form colonies. It is hoped that an appreciation of regulatory abnormalities in patients can contribute to improved therapeutic approaches to their diseases.